Leaking Radiator Cap

[jbow03]

When I first tried out the cooling system, the car was on. Jack stands and idling. It would get up to temperature. The cooling fans would turn on and the temperature would pull down. Extra coolant would go into the overflow tank would’ve got hot and then would get pulled back into the system to cool down.

This week I took the car out to go kart for the first time and noticed that as it now gets significantly hotter, coolant spits out from the radiator cap. This occurs after the engine gets warm and I’m running around the neighborhood.

Any ideas? I still have the 20 pound cap on that came from factory five. I’ve noticed that some people will put a lighter cap on.
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[BornWestUSA]

It sounds like you may still have some air in the system?

Does the radiator cap have two rubber seals, the center one with the spring and the outer one below the tightening surface?

Once all the air is out it should stabilize.

My t'stat also has a 1/8" hole drilled into it to assist bleeding.

I use one of these to make a high point for the bubbles to exit:

https://www.amazon.com/Lisle-24680-Spill-Free-Funnel/dp/B00A6AS6LY?crid=9NTE9SV6RQZ9&dib=eyJ2IjoiMSJ9.d809N_BFSVg4qNeaHOO9SYEw2496lLACj gXlenX5p2xX2Q3LGfS7tbzDQoIOSJyWIntNSxIIOPn1Vi6TrJQ BX1TpHkEJRwMdBAZSHhTzZuOq9WE-6o8UPn4NOMPg27597mkPp4MQy27_XGdEuQ4RzB9lHG66pgrAX7 j-hPq8i4PmUMTuhVvf8MZCu9obaQXtokmW_DNQA9NV5DbU63sueu JOVFZQuC1MUpzAbR_C4QsEXbhJqiwfkiZ9ElVgzkbt9cWf4WE_ nn4G3t-YJgD7DVXG0YB2YgfDDzPUDaPs2QQ.VQlJ5D9rDsGQZFueyftk8 Ia-DVznLoSq-cDaXQPLPQE&dib_tag=se&keywords=lisle%2Bradiator%2Bfunnel&qid=1748197483&sprefix=lisle%2Bradiator%2Bfunnel%2Caps%2C198&sr=8-1&th=1

[Mike.Bray]

I would be tempted to try a different cap, a name brand of known quality. No slight intended towards Factory Five as they have to make a profit but some of the stuff they provide in the kits is less than top quality.

The 1/8" hole in the thermostat is a good idea also.

[jbow03]

Ok, I believe I had the hole in the thermo.

So keep driving and monitoring levels and things should settle in? When I get the new cap, same weight? I’ve seen folks go lighter to 12lb or so.

[egchewy79]

The weight on the caps dictate how much pressure the system sees before the vent opens allowing fluid to spill into your overflow canister. The larger the # the more pressure and the higher the temps can reach before the valve opens. I have a #16 cap on mine.

Here's a good article explaining the different caps
https://www.dewitts.com/blogs/news/13852841-what-pressure-cap-rating-should-i-use?srsltid=AfmBOorfDNIhVf6gaXtQaEVOk1YpeSqm_SC1h_ 1zI5RElCX8G6soapfP

[RJD]

Make sure your overflow tube fitting at the radiator cap isn't blocked. I had the same symptoms as you and it turned out a polishing bead had gotten lodged there.

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[gbranham]

Also, the tabs on the radiator cap that grab onto the t-filler...bend them "up" a bit, so your cap fits the t-filler tighter. I've solved a leaky cap that way in the past.

[CraigS]

Not sure this applies w/ your T-filler but there have, over the years, been some where the surface inside, that the cap should seal on, was not machined properly. I am also w/ RJD although not specifically. W/ a properly operating overflow system there should never be fluid leaking where yours is. Any fluid getting past the pressure seal should all go to the reservoir.

[AC Bill]

Have you checked the coolant level after it's cooled? It sounds like the overflow system is working correctly, so the level should be still close to full. If it has dropped down significantly, perhaps it's been losing coolant over time, un-noticed, and an air pocket has formed.

[jbow03]

Coolant level when hot is at the overflow tube and it has dripped over a bit now.

When cool, it drops down about 1/3 the length of the container.

[rich grsc]

The recovery tank is over full. When cold 1/3 to 1/2 full